I'm probably not the best person to reply as I've not got on well with mid lengths recently however my problem is more one of getting used to the ride style. If you are used to a shortboard maybe you're not making the most of the early drop and still looking for the more peaky part of the wave? Its not so necessary and will give you less time to correct your position. Do you only have the problem on hollow waves? Try getting used to getting in as early as the board will let you on slower waves- keep your weight forward as you feel the wave start to pick you up then when you pop youve got time to adjust yourself before the wave gets critical.Start by popping back slightly more than on a shortboard as its easier to have to adjust weight forward than back. If you are surfing a wave that needs a quick pop with a late drop you're gonna have to have a good idea of where the sweet spot is on the board and that takes a bit of time with a longer board. Also don't be scared to have alot of the board out in front of you so you can work it from the back. A few shortboarders I know who have strugggled with longer boards seem to get the fear a bit seeing that much nose out ahead of them as they take the drop. It just takes a bit of getting used to

in hollow waves I struggle with getting down the face too, what worked for me was ditching the step up and just surfing a regular shortboard, forces you to put in a few good hard paddles and take off right in the pocketnot so useful if you've got your heart set on a longer step up for paddle power, but a shorter step up designed for that sort of approach might be the answerwhen the waves get good is not when you want to start making big changes to how you approach a wave

A lot of what jay P says,also take a bit of time paddling around to find the sweet spot,not quite as easy to find on a longboard as a shortboard,keep going forward until the nose sinks while paddling then i always moved back a couple of inches,if I ever think I'm going to pearl it i will arch my back up as if I'm trying to lift my chest to take the weight of the nose

fair play, once it gets that big and hollow surely all you need is the weight of your bollocks pulling you down the face and you're in honestly having never had the same struggle I don't know quite what to suggestI suppose I keep a forward placement when paddling and just put my hands a tiny bit further back when taking off so I get to my feet further back on the board once up

there's a sweet spot for every board, try spending more time on those boards in less heavy waves, and also spend more time on longer boards in general, might help get the feel for that sweet spot